1. Field of the Invention
The present invention generally relates to a method for calibrating a parameter of an integrated circuit (IC) and more particularly, to a method for calibrating a parameter of an IC using an external device so as to calibrate an analog control parameter of an internal analog circuit in the IC.
2. Description of the Prior Art
With the development in semiconductor technology, the demand on the accuracy in output signals from the electronic circuit increases. However, inaccuracy inevitably happens in manufacturing processing. For example, in an RC oscillation circuit 11 in an IC 1 (in FIG. 1), the inaccuracy in the output RC oscillation frequency may exceeds ±20% Therefore, it is required to reduce the inaccuracy to an acceptable range using a calibrating step.
Please refer to FIG. 1, which is a conventional IC layout for calibrating a parameter of an IC. There are provided with a plurality of trim pads (Trim Pad 1, Trim Pad 2, . . . , Trim Pad n) inside the IC. When the output RC oscillation frequency of, the RC oscillation circuit 11 is detected to go beyond a pre-determined range, hardware is fused to calibrate the output and reduce the inaccuracy to an acceptable range. However, the cost of hardware is increased for an IC demanding high accuracy because more fuse pads are required.
Please refer to FIG. 2, which is another conventional IC layout for calibrating a parameter of an IC. Before the IC 2 is ordered to be shipped, an internal analog circuit 22 in the IC 2 is tested in a testing mode, and correction is made according to the tested results. An I/O unit 24 is used to program a non-volatile memory 23 in the IC 2 with the corrected calibrated value. Generally, the internal analog circuit 22 includes an RC oscillation circuit 221 and a low-voltage detection circuit 222. Moreover, if the non-volatile memory 23 is implemented using a low-cost erasable programmable read-only memory (EPROM), the calibrated value programmed in the non-volatile memory 23 may not be optimum because the EPROM can only be programmed once. If the non-volatile memory 23 is implemented using a high-cost electrically erasable programmable read-only memory (EEPROM) or other re-programmable non-volatile memories, the non-volatile memory 23 can be re-programmed when the calibrated value programmed in the non-volatile memory 23 is not optimum because the EEPROM can be programmed repeatedly. However, the cost for EEPROM is much higher than that for EPROM.
Therefore, there exists a need in providing a method for calibrating a parameter of an IC with high accuracy and low cost.